This invention relates to an electrophotography photosensitive member used for a copying machine of an electrophotographic type, a photo printer or the like, and a method for fabricating the same.
Conventionally, in an electrophotography photosensitive member, the function-separated type of the electrophotography photosensitive member is widely used which comprises different material layers. One such layer is a carrier transport layer for transporting carrier and the other is a carrier generation layer for generating carrier due to optical pumping. By selecting the material depending on the function of the material, an excellent photosensitive member having a high sensitive electrophotography property can be provided. Moreover, the most suitable combination of materials can be investigated using various materials having different properties such as mechanical strength, thermal stability, printing durability and manufacturing cost.
Organic materials have become of major interest and are actively investigated because there are various kinds of organic materials.
There are many electrophotography photosensitive materials comprising a carrier transport layer and a carrier generation layer which utilize organic materials. For example, there are combinations of methyl squaric acid and triaryl pyrazoline, combinations of dyanblue and oxadiazole, combinations of perylene pigment and oxadiazole, combinations of bis-azo pigment and styrian anthracene, and the like.
Besides, combinations, inorganic materials are also used as the carrier generation layer. For example, there are the combination of amorphous silicon as the carrier generation layer and organic semiconductor material as carrier transport layer which is disclosed in Japanese Laid-open Patent Application No.54-143645, and the combination of amorphous selenium and polyvinylcarbazole. These combinations belong to the function-separated type of photosensitive materials.
In the function-separated type of photosensitive materials comprising combinations of organic materials, there are many problems such as the printing durability is poor, the lifetime is short, and the reliability is poor.
In such photosensitive members using organic materials, the carrier generation layer, the carrier transport layer, and moreover, a surface layer for increasing the hardness of the surface or the like are formed on a sheet-like substrate of an endless belt or the like, or on a cylindrical drum made by a cutting method or a molding method such as an impact method. In this case, it is necessary to uniformly each form of the layers in accordance with the process necessary for producing the electrophotography.
The methods by which each of such layers is formed, include a dip coating method, a spray coating method by a spray gun, and an US-spray coating method using ultrasonic waves. However, these methods require large plant and equipment investment.
In the combination of the inorganic materials as the carrier generation layer and the organic materials as the carrier transport layer, attempts to use an inorganic carrier generation layer having a large degree of hardness as the surface layer, in order to improve the printing durability. However, in order to maintain the desired properties, many carrier generation layers having an excellent printing durability require heating of the substrate or require a process such as the method using plasma by which the surface is heated to a high temperature. In such cases, since the organic carrier transport layer has an inferior heat resistance, a photosensitive member having desired properties cannot be obtained.
Of such methods described above, Japanese Laid-open patent application No. 55-90954 and Japanese Laid-open patent application No. 60-59353 discloses that PPS (poly-p-phenylene sulfide) film used as the carrier transport layer is an excellent material which can be cheaply produced, and deposited as a polymer film having a high carrier mobility.
It is necessary for the electrophotography photosensitive member to have a small dielectric constant, a large mobility, a large carrier lifetime, and a capacity for generating large amounts of carrier in order to have a high sensitivity. Therefore, in the function-separated type of the photosensitive member, it is desirable to combine a carrier transport layer having the large mobility and the large carrier lifetime and a carrier generation layer having the capacity for generating large amounts of carrier. However, it is necessary to include a carrier injection between both layers, even if each of the layers satisfies the required conditions stated above. Moreover, it is necessary that the properties such as abrasion resistance, a capacity for accepting carrier, and the like, which are required to the process of the electrophotography, be present.
Japanese Laid-open patent application No. 55-90954 discloses PPS is formed into thin film. The capacity of the PPS for transporting carrier of PPS is improved by the method of vacuum deposition, by which method the resulting film is applied to the carrier transport layer. However, the resulting carrier transport layer has a small capacity for transporting carrier, and does not have a sufficient sensitivity and a good residual electric potential. Moreover, the time required for making the film is long because of the vacuum deposition method. Therefore, the resulting photosensitive member is of high cost among the photosensitive members using organic materials. Furthermore, the resulting film does not have sufficient hardness nor sufficient printing durability.
Japanese Laid-open patent application No. 55-90954 discloses a photosensitive member that can be cheaply produced by applying the PPS film to the carrier transport layer. However, the photosensitivity does not reach the level of practical use of the electrophotography photosensitive member, because of the insufficient capacity for transporting carrier.
Moreover, the function-separated type of the photosensitive member using organic materials has a problems associated with miniaturizing the electrophotography apparatus because this photosensitive member requires negative charging. Furthermore this photosensitive member has a problem because it generates ozone.